The radioimmunoassay (RIA) laboratory supports epidemiological and metabolic studies which address the role of islet cell function and insulin resistance in the development of obesity and diabetes in the Pima population. RIA's for insulin, C-peptide, glucagon, and glucagon-like immunoreactivity (GLI) are performed in conjunction with several of the clinical studies and are used to investigate islet function and its regulation in obesity and diabetes.